An estuary is a coastal wetland where freshwater that flows from rivers and streams mixes with the saltwater from the ocean.

Or more simply put, an estuary is where the river meets the sea.

Here, the Tijuana Estuary is made up of freshwater from the Tijuana River that connects with the saltwater of the Pacific Ocean creating a large wetland habitat dominated by low lying vegetation known as a salt marsh. This connection of waters happens at the rivermouth, and because of it, the water level in the estuary rises and falls with the ocean tides. Water, as well as fish, or anything else in the water can come in and out through the rivermouth making this area highly attractive for many species of birds. The Tijuana Rivermouth is the only one in San Diego County that naturally moves with storms and wave action because it is not bisected by a railway or highway like the other rivermouths of the estuaries in the county.

Other examples of estuaries are bays, swamps, mangroves, and bogs. Learn more about why estuaries are important and find out more about our nation’s extraordinary estuaries at the NERRS Estuary Education website.

We have over 370 species of birds, brush rabbits, jack rabbits, lizards, squirrels, grey foxes, and coyotes. In the Border Field area you may still find the bobcat but it is unusual. We do have rattlesnakes but they are rarely seen north of the river and are more common at Border Field. Stay on the trail when hiking. The California kingsnake, a natural predator of the rattlesnake, is commonly seen when the temperature is warm enough. The California kingsnake is not dangerous to humans. Learn more about plants and animals of the reserve.

Generally during low tide, on the North McCoy trail, you will usually see a good variety of shorebirds feeding on the tidal mudflats, especially during fall/winter migrations. High tides will often flush the Ridgway's Rail into higher areas of the marsh. The brackish ponds reached from the 5th and Iris Street trail offer a good look at migratory waterfowl and many other bird species found at the Reserve. The river mouth is an excellent place to see a variety of birds especially California Brown Pelicans. View the Tijuana Slough Bird List.

The Ridgway's rail is usually seen on the North McCoy Trail near the wooden bridge not far from the Visitor Center. It can be observed during low tide foraging along the banks of the channel, or taking a quick bath. It can also be seen during a high tide when it is flushed out of hiding.

The Ridgway's rail is dark brown with a cinnamon colored breast and white under the tip of its short tail. It looks like a marsh hen. Ridgway's rail chicks are all black.